The present invention relates to a transforming circuit, and more particularly to a transforming circuit capable of transforming signals corresponding to different frequency bands.
In a communication system, a transformer balun (balanced/unbalanced) is a device installed in the transmitter and the receiver, and is used to convert single ended signals into differential signals and vice versa. Conventionally, one transformer balun is always designed to convert a signal corresponding to one specific frequency band. In other words, the coupling coefficient has the largest value when the signal is in the specific frequency band, and the coupling coefficient may be worse when the signal is outside the specific frequency band. Accordingly, in a multi-mode communication system, a plurality of transformer baluns is used for converting signals corresponding to different respective modes. As one transformer balun may occupy a relatively large area, installing the plurality of transformer baluns into the multi-mode communication system can cause the manufacturer significant problems. Therefore, providing an efficient and low cost transforming circuit for the multi-mode communication system is a significant concern in this field.